Group 2 Plymouth Field Course
WINNIE THE POOH
A small group of 5 students travelled to the upper Tamar estuary aboard Winnie the Pooh, the smallest boat of the fleet involved in the field course, with Skipper Robin and Technician Graham.
The aim of this trip was to collect samples to complement those collected in the lower estuary by the group on Falcon Spirit, giving a view of the continuum of environmental conditions present in the estuary. The expedition set out from Saltash Pontoon at 8:02 UTC, where the third and smallest group remained to sample. We made the best of the flood tide (high tide at 10:44 UTC) by first travelling all the way up to Calstock. Station 1 was settled a little up beyond Calstock at 10:25 UTC, where the lowest salinity was recorded; and then back down the estuary stopping at regular intervals on the way to sample the water with the CTD, handheld Niskin bottle, and sometimes tow the plankton net. The last station was at the confluence of the river Tamar with the river Tavy, ‘Station B’, at 13:58 UTC
Temperature was plotted against salinity and depth. Salinity was used as a conservative
measure of the river-
The actual data points are indicated by squares on the contour graph. Therefore,
the temperatures that fall away from these points have been generated by the software
and do not represent samples, so cannot be assumed to be accurate. For example, where
salinity was less than 16, the maximum depth was only 4m -
Regardless, the contour graph is still indicative of the major trends, and is a useful tool in visualising this. It is clear that the warmer surface waters has been heated most extensively by the sun to up to 23.5oC, whilst the deeper (beyond 3m), saltier (above 30 PSU) water intruding from the ocean is much cooler, down to 19.5oC.
High oxygen saturation (over 100% -
The higher salinity, more oceanic waters show greater mixing and/or greater photosynthesis. To identify the cause, further data would have to be compared such as chlorophyll (a common photosynthetic pigment) and richardson number (an indication of mixing). However, it is likely an indication of photosynthetic activity as the increase is seen to the bottom of the water column (5m).
The high oxygen pocket at 1m, 23 PSU, can likely be disregarded as the actual data points (indicated by black dots) show data of ~200%, whereas the pocket assumes dissolved oxygen up to 300%. The increased oxygen saturation in this location is likely due to physical mixing (as due to wind stress, boat wake etc) as it does not penetrate further than 1~2m.
Dissolved Oxygen
Temperature
The views and opinions expressed are those of the individual and not representative of the University of Southampton or the National Oceanography Centre.
As we travelled down the estuary, the salinity and temperature were regularly tested by a basic cynometer to assure intervals of approximately 2 psu between each station. Once the station was shouted, a multiparameter cynometer was deployed to record depth profiles for temperature, salinity and dissolved oxygen. At the same time, the horizontal Niskin bottle was manually lowered, collecting samples for nutrients and chlorophyll. Water samples for upcoming nitrate and phosphate analyses were stored within the same glass bottle, whilst samples to study silicon were stored apart in a plastic bottle to avoid interactions with the glass (bottles are mainly made of silica and silicates). Filtering was required in order to test chlorophyll concentrations in the water surface. Three replicates were made for each station, introducing the filters in acetone solutions for later examination.
During the investigation, three locations of interest were chosen to tow the plankton
net: the highest, lowest and one in-
Fig 2 -
Fig 2 -
